Every inboard have an impeller in the sterndrive?

[colo-pr]

Hi guys,

I have replaced impellers in outboards before but now on my Mercruiser 5.0 MPI with Alpha drive I am so confused if it has an impeller I have to replace/maintain as a regular maintenance too. Looking at the Service Manual I still confused because the manual talk about different models and in the illustrations they show an impeller. I know mine has a water pump in the engine for sure but when have a water pump, it uses an impeller too (perhaps to move water up so the water pump can pick it up?) Im trying to avoid remove the lower unit just to check.

Thanks in advance.

 

[b_arrington]

All Alpha drives have a raw water impeller in the lower unit, like an outboard. Bravo drives have the raw water pump mounted to the engine and not in the drive leg.

The engine will also have a belt driven circulation pump. This moves the cooling water around the engine passages. The impeller driven pump delivers cooling water to the engine and then the belt driven circulation pump pumps it throughout. The circulation pump has a metal impeller that does not need regular replacement as with the raw water impeller.

 

[colo-pr]

All Alpha drives have a raw water impeller in the lower unit, like an outboard. Bravo drives have the raw water pump mounted to the engine and not in the drive leg.

The engine will also have a belt driven circulation pump. This moves the cooling water around the engine passages. The impeller driven pump delivers cooling water to the engine and then the belt driven circulation pump pumps it throughout. The circulation pump has a metal impeller that does not need regular replacement as with the raw water impeller.

Thank you so much, that's what I thought. Well, something more to add to my list of maintenance, I hope the lower unit is not that hard to put back up like a bad experience I had with an old Mercury 140hp outboard that took me days of playing until finally was able to put it back up, mostly because of the shifting gear rod.

Thanks so much for the quick response.

 

[BillK2632]

The alpha impeller change is pretty much the same as an outboard. I would remove the drive to do this, it is a PIA to split the lower and reinstall with the drive on the boat. Build a drive stand and do the work that way.

 

[colo-pr]

The alpha impeller change is pretty much the same as an outboard. I would remove the drive to do this, it is a PIA to split the lower and reinstall with the drive on the boat. Build a drive stand and do the work that way.

Sorry, I may explained my self wrong, I am not taking the drive out, I was referring to the lower unit. The way I'm used to do it is removing the lower unit from the drive, thats the easy part but when have to join it back it can be tricky in my experience, the water tube, the gear rod, etc. mostly if by mistake you moved the gear rod to a different position. I will try the stand idea, should make it way easier. Also, how you do it? with the gear in neutral, reverse or forward? I've read all options, just watched a video of a guy recommending in forward so the shaft doesn't move, but I still unsure (Maybe I dont understand it right) what is the best way.

 

[BillK2632]

I always remove the drive and put it on a stand I built. Very difficult to attach lower to upper while still on boat. You cannot see to get the water tube liners up. Always in foreword removing and installing drive.

 

[JVM225]

Removing the drive from the transom and reinstalling it is fairly easy and it gives you the chance to inspect other maintenance items inside the transom assembly (Bellows) too while the drive is off.

 

[colo-pr]

I will have to look online how to remove the drive, never done it and looks kind of scary for me.